This invention relates to a sealing arrangement for effecting a seal with a rotatable shaft.
A variety of different types of seals for rotating shafts is widely known and available for use in numerous arrangements to control and attempt to prevent leakage of oil or lubricant or other liquid past the seal. In a typical arrangement, a seal of rubber or PTFE in the form of an apertured disc is fitted about the rotating shaft so that the aperture forms a tight fit about a circumference of the shaft to provide a sealing lip at the point of contact with the shaft.
The sealing lip may have associated therewith a variety of sealing aids so that any oil in the vicinity of the lip or, more particularly, any oil which escapes past the lip is urged back to its correct side of the sealing lip. Such aids can commonly take the form of protrusions or grooves on the surface of the seal in the vicinity of the sealing lip which act to "fling" any oil impinging on them in a predetermined direction during rotation of the shaft. Such aids can be varied from seal to seal so that they can act unidirectionally, i.e. when the shaft rotates only in a single direction or bi-directionally, i.e. when the shaft rotates in either direction.
Although such shaft sealing arrangements can operate satisfactorily in many instances, there remain undoubted problems in effecting an adequate seal in certain cases. For example, in some specialist applications, there is often a need to employ oils or lubricants having certain properties which may give rise to particular problems in use with the shaft seals referred to above.
In the vacuum industry in particular, certain oils tend to be used having particular properties which are required in that industry. For example, the oils generally are often required to be chemically very inert and have a low vapour pressure. Particular oils that have been used are perfluoropolyethers available, for example, under the Trade Marks FOMBLIN and CRYTOX; however, such oils tend to possess low surface tension properties which can make them particularly difficult to seal with known shaft sealing arrangements in particular.